The ELT in numbers

Main mirror diameter: 39 metres

Light collecting area: 978 square metres

39-metre diameter

With its main mirror as large as 39 metres in diameter, this will be the largest telescope to observe in visible-light. It will be four to five times larger than the present-day state-of-the-art facilities of this kind, and will collect about 15 times more light. It will also be much larger than the two other extremely large telescopes in planning, the Thirty-Meter Telescope and the Giant Magellan Telescope.

Almost 800 segments

It is not possible to build such a large mirror in one piece. Instead, the 39-metre diameter primary mirror will be composed of 798 hexagonal segments, about 1.4 metre wide and 5 cm thick. The whole concept of the telescope is to be modular, so that pieces can be manufactured in large quantities, thereby drastically reducing the cost. Only this approach makes the ELT possible within a restricted budget.